Considerations about how we should use animals, if at all, have pervaded human society for millennia. However, it is in the modern era that the necessity to use animals for food and many other uses is most strongly debated. As well as animal welfare and ethics concerns, people are concerned about the inefficiency of using animals to provide food for a growing human population, the associated pollution with intensive animal production systems, and the disease implications. This chapter reviews the major uses of animals and evaluates whether there is any justification for doing so.